The sub sea oil and gas industry has very critical safety functions depending on the capability to shut certain process valves, thus functioning as Emergency Shut Down (ESD) valves, on either loss of pressure integrity of the installation or on partial or complete loss of control and/or communication functionality in a sub sea production system. This capability is quantified and is referred to as Safety Instrumented Level (SIL) and is subject to very specific and rigorous statutory and operator functional requirements.
There is thus a market in the sub sea oil and gas industry for high reliability actuators for actuation of several mechanisms of critical importance, all characterised by a need for dependability of the “shift position” operation after prolonged service in the normal operating mode (steady state production).
In production systems based on conventional electro-hydraulic control such functionality as described above is found e.g. in ESD type control valves. These valves can be located topsides or sub sea and are characterised by permanently energised solenoid pilots in the normal operating mode. In the ESD mode the electrical power is either deliberately or inadvertently switched off, leading to a safe condition of critical process/ESD valves in the pressure containment system, the latter being controlled by said ESD directional control valves (DCV).
The use of solenoids to provide the transformation of electrical power into force and motion is quite universal in the sub sea oil and gas industry. Solenoids are robust and reliable devices but produce very little force per ampere-turn, especially in the early phase of the stroke. This has led to hydraulic directional control valves (DCVs) being equipped with a poppet type solenoid preamplifier to shift the slider in the valve (the latter being typically a high friction shear seal design) in order to provide sufficient force to overcome dynamic and static friction forces.
These poppet valves are particularly prone to failure by fluid particulate contamination by virtue of the high pressures and thus the very small dimensions of the poppet being required in view of the low mechanical force available from the solenoid.
Similarly, attempts at providing a fail safe mechanism for e.g. electric actuators tend to either work with low mechanical forces or large magnetic devices.
Prior art is very comprehensive. As an example of a recent approach to electrical actuation for a down-hole safety valve application US 2004/01173362 may be referred to.